Nickel crystallizes in an FCC lattice with an atomic radius of 124 pm
CHEMISTRY · Single correct · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Nickel crystallizes in an FCC lattice with an atomic radius of 124 pm. In this lattice, the maximum atomic radius that can occupy (without significant distortion) an octahedral hole is approximately 0.414rNi, and for a tetrahedral hole is 0.225rNi. A metallurgist adds 4.0 atomic % carbon (atomic radius 67 pm) to molten nickel and allows the alloy to solidify.
Which statement is most consistent with how the carbon atoms will be incorporated into the solid?
(a) Carbon atoms replace nickel atoms because their atomic radii differ by less than 15\%, producing a substitutional solid solution.
(b) Carbon atoms occupy tetrahedral interstices because 67pm<0.225rNi, so the lattice is only slightly distorted.
(c) Carbon atoms occupy octahedral interstices even though 67pm>0.414rNi, so their presence strains the FCC lattice, forming an interstitial alloy.
(d) Because of the large size and chemical differences, carbon is essentially insoluble in nickel and will precipitate as a separate phase.